Can an EPOS audit trail prove what changed?

HMRC is consulting on proposed EPOS/MPOS software standards until 18 August 2026. The proposed package includes an unalterable and complete transaction log with individual transactions and adjustments indelibly linked in an encrypted chain. These are consultation-stage proposals, not current final standards.

The practical engineering question is broader than the policy context: when a sale changes, does the system preserve the original state, record the adjustment explicitly and keep the relationship between both states traceable? A final value by itself may be easy to read, but it does not necessarily explain what changed or how a reviewer can reconstruct the path.

A simple review rule

Use three visible states:

1. Original — retain the first recorded transaction.
2. Adjustment — represent the correction as a distinct event.
3. Linked history — preserve the relationship so the change can be followed later.

This is an audit-trail design test, not tax advice and not a claim that the consultation proposals are already mandatory. The HM Revenue & Customs consultation is the source for the policy context; the implementation process and timeline have not yet been decided.